Answer:
Say you have a key in a dictionary, or a key in a 2-d list. When you insert(), you are destructively iterating the original list and modifying it to reflect the insert() component. In order for the key to get lost you would have to do say insert(len: :1) which would remove the second key and therefore cause it to get "lost" because it will be destructivsly removed from its assignment and replaced by whatever you choose to insert.
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